Evaluation of current DEM accuracy for Condamine Catchment

Evaluation of current DEM accuracy for Condamine Catchment

[Abstract]: A digital elevation model (DEM) is one of the most important datasets for catchment management and planning. It provides elevation information that is useful for many environmental applications including hydrologic modelling and flood management planning. Currently, the most comprehensive catchment wide DEM in the Condamine Catchment is a dataset derived from 1:100,000 topographic mapping. It is identified as the Department of Natural Resources and Water (NRW) DEM and it has an estimated average accuracy of approximately 10m vertically based on a 25m horizontal grid. The Shuttle Radar Topographic Mission (SRTM) derived DEM is also available for this catchment. It has a horizontal resolution of 87m and a vertical accuracy of about 16m. The accuracy of these DEMs may not be suitable for all application areas. Therefore, accuracy assessment of current DEM was deemed necessary. In this study existing ground survey marks were used as ‘true’ elevation data for DEM accuracy assessment. For assessment purposes, the catchment area was classified into flat, moderate and steeper slope categories and each category was evaluated separately. Elevation data corresponding to the existing survey marks were extracted from each of the above DEMs. Differences were calculated between the survey marks and the elevations extracted from the DEMs. These differences were grouped into several error ranges for each slope category and each DEM type. The result indicated that the NRW 25m DEM has better than 10m accuracy at 90% confidence level. The SRTM 87m DEM over the same area has proven to be slightly better with a 95% confidence of better than 10m. However, the accuracy assessments of these DEMs vary over the different slope categories and land use utilization.

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